Process for the preparation of mineralfilled papers



United States Patent Ofiice Patented June 10, 1958 PROCESS FOR THE PREPARATION OF MINERAL FILLED PAPERS Irving J. Gruntfest, Cheltenham, Pa., and David B. Fordyce, Moorestown, N. J., assignors to Rohm & Haas Company, Philadelphia, Pa., a corporation of Delaware No Drawing. Application April 10, 1956 Serial No. 577,195

4 Claims. (Cl. 92-21) ness to the paper. 7

In the production of filler papers, appreciable amounts of the fillers pass through the screen during the deposition of the paper or other fibrous sheet or molding formed of the fiber-filler suspension. The so-called white-water which thus passes through during the deposition contains substantial amounts of the filler and is either discarded in plants using a so-called open system or is re-circulated for re-use in the so-called closed system. When the white-water is discarded, there is not only an economic loss of the filler but also a possible stream polution problem. Even with the re-circulation technique, some white-water is eventually discarded with consequent loss of filler..

In order to reduce the amount of filler which passes through the screen during the deposition of the fibrous structure, various retention agents have heretofore been used including alum, glue, polyacrylamide, and the condensation products of urea with formaldehyde and polyalkyleneamines. These retention agents have provided some benefit but have various disadvantages. Certain of them, such as alum, cannot be used with calcium caraliphatic ketene dimers, described in U. S. Patent 2,627,-

477, can only be efficiently used if the filler paper is made in the absence of alum. Another disadvantage of previous processes for making filler papers is the tendency to form one-sided sheets, that is, sheets in which the filler is largely trapped and retained on the top side of the fiber mat.

In accordance with the present invention, the deposition of formed fibrous structures, such as paper from aqueous suspensions containing the fiber and the mineralfiller, is greatly improved by the incorportion in the suspension, during the deposition or prior to-the deposition, of extremely small amounts, relative to the amount of fiber and/ or filler in the aqueous suspension of improved retention agents hereinbelow defined.- The improved retention appears tobe the result of a bridging action between thefiber and the filler eifected by the retention agent. Possibly the retention agent acts as a molecular 2 bridge between the fiber and the filler. The retention agents of the present invention exhibit a high efficiency over a wide variety of pH conditions from acid through neutral to the alkaline side up to a pH of about 12 and especially from pHs between 3 and 10. Generally, a substantially lesser amount of the retention agents of the present invention may be used as compared to the amounts of retention agents heretofore used to obtain comparable efiiciency. Alternatively, greaterefiiciencies are obtained by using small amounts of the new retention agents than can be obtained with the agents used heretofore regardless of how much of them is used. Because of the adaptability of the new retention agents to be used under a wide variety of pH conditions, filled papers can be obtained which are adaptedto receive a wide variety of sizing materials including rosin sizes generally applied under acid conditions, or waxes, and especially higher aliphatic ketene dimers, such as hexa-decyl ketene dimer or any of the others mentioned inthe above-cited patent which are especially useful whenapplied to papers prepared under neutral or alkaline conditions. In some cases, the tendency towards two-sidedness in filled sheets may be reduced using these new retention agents.

The retention agents of the present invention are high molecular weight water-soluble polymeric substances of the. group consisting of certain linear polymeric esters containing basic amine groups, their salts, and quaternary ammonium'compounds formed therefrom. These polymeric esters are the linear polymers of at least 10 mole percent, and preferably at least 50 mole percent (of the total polymerized units therein) of monomeric units having the formula I --OH2C R -A-NRR in which R is H or CH R is H, CH or C H and R2 is H, CH3, 0]. C2H5 Preferred polymers are those in which R is a methyl group, A is an ethylene group and both R and R are methyl groups. These linear polymers of the aminoalkyl esters of acrylic or methacrylic acid must have an average molecular weight of at least 100,000 and preferably at least 250,000 and may have as high a molecular weight as is possible to attain, such as several million.

Water-soluble as used herein is intended to include polymers which either in their free amine form, their salt or quaternary form produce true solutions or colloidal solutions when they are present in the aqueous media in the small proportions hereinafter specified.

The salts of these polyesters may be those of any organic or inorganic acid, such as hydrochloric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid and so on. The quaternary compounds may be of any of those formed by quaternization with any suitable alkylating agent (which is herein intended to include aralkylating agents and substituted aralkylating agents), such as methyl chloride, ethyl chloride, benzyl chloride, allyl chloride,

least one ester unit (or a salt or salts thereof) having the structure of Formula I and about 45 to mole pereen;

acrylate and methacrylate and their salts.

dispersion or suspension.

cal action alone may be resorted to in order to effect the dispersion or suspension thereof in the aqueous medium.

3 of at least one quaternary unit having the structure of Formula II:

where R is selected from the group consisting of H and CH and is preferably CH A is selected from the group consisting of -(CH (CH and -CH CH(CH R is selected from the group consisting of methyl and ethyl, R is selected from the group consisting of methyl and ethyl, R is selected from the group consisting of benzyl, lower alkyl having 1 to 4 carbons, fi-hydroxyethyl, fl-hydroxypropyl, and v-hydroxypropyl, and X is selected from the group consisting of hydroxyl and negative, salt-forming atoms and radicals. Examples of these negative radicals include halides, such as chloride, bromide and iodide, sulfate, e. g., the methyl sulfate anion, acetate, propionate, and so on. The units of Formula I may be in the form of a salt, such as the hydrochloride, hydroacetate, etc.

The water-soluble linear polymers of the present invention may be made by the direct polymerization of the aminoalkyl esters of acrylic or methacrylic acid or their salts or quaternaries to form a homopolymer of any one of them or a copolymer of any two or more thereof. Specific examples are the polymers of dimethylaminoethyl aerylate and methacrylate, diethylaminoethyl acrylate and methacrylate, 3-dimethylor 3-diethylamiuopropyl acrylate and methacrylate and Z-dimethylaminoisopropyl In addition, polymers of the invention may be produced by copolymerizing the aminoalkyl ester of acrylic acid or methacrylic acid with one or more other mouoethylenically unsaturated copolymerizable substances, containing a group, and especially those having a terminal group CH =C=, such as vinyl acetate, vinyl chloride, acrylonitrile, acrylic acid, methacrylic acid, methacrylonitrile, acrylamide, methacrylamide, styrene, ethylene, isobutylene, tetrafluoroethylene, chlorotrifiuoroethylene, or with any ester of acrylic acid or methacrylic acid such as their esters with aliphatic alcohols from 1 to 18 carbon atoms of which methyl acrylate, methyl methacrylate, tert.-butyl methacrylate, n-oetyl methacrylate, and octadecyl meth- When quaternaries where a comonomer is of a type which tends to form hydrophobic polymers, the proportion of such comonomer should not be so large as to produce a copolymer which is notwater-soluble to the extent defined above.

The utilization of the retention agents of the present invention in the preparation of filled papers may be accomplished in several ways. In the preferred manner, the retention agent is added to the suspension containing the fiber and filler suspended or dispersed therein. In the preparation of the fiber/filler suspension, either of these two insoluble substances may be dispersed in the aqueous medium before the other-and, if desired, a wetting or dispersing agent may be employed to assist the On the other hand, mechani- Alternatively, a pigment suspension or dispersion may be prepared in water and the retention agent may be introduced into this dispersion or suspension before adding it to an aqueous suspension of the fiber. The conventional consistencies of the pigment dispersion or suspension and/or of the fiber suspension may be employed. For example, the fibrous suspension may have a consistency of anywhere from about 0.1% to 6% fiber on the weight of the suspension. When beaten pulps are used, the filler and retention agent may be added to the pulp suspension while it is of the consistency, generally about 3% to 5% or 6%, of the pulp during the beating operation. Thereafter, the aqueous system may be diluted with water to provide the desired consistency that is conventionally used during deposition, which may amount to from 0.01% to 0.5% fiber on total suspension weight. If desired, the pulp may be diluted approximately to the consistency at which the deposition is to be made and the pigment and retention agent thereafter added.

The amount of filler may be from 1% to 50% by weight on the weight of fiber (based on dry weights) and the amount of retention agent may be from about 0.01 to 1% by weight thereof on the weight of the dry fiber. When large proportions of fillers are used, based on the weight of the paper fiber, it is preferable to employ an amount of retention agent between 0.1 and 1.0%, based on the weight of filler.

The conventional inert filers or pigments may be used, such as clays, titanium dioxide, barytes, blanc fixe, talc, calcium carbonate, and the like. The filler is in finely divided form and may be dispersed directly into the fiber suspension with the aid of a dispersing agent or by mere mechanical action, but it is preferably pasted in a small amount of Water with from 0.01 to 1% on the weight of the filler of a dispersing agent. Typical dispersants are sodium hexametaphosphate, sodium tetrapolyphosphate, formaldehyde condensates of naphthalene sulfonates and the sodium salts of 50:50 mole ratio copolymers of maleic anhydride with styrene, diisobutylene and the like.

Any suitable pulps may be used for making the fibrous products including bleached and unbleached pulps. They may be sulfite, kraft, soda, semi-chemical, groundwood, rag pulp, rope pulp, jute pulp, and so on.

Where deposition on the acid side is desired, the fiber suspension may include alum or alum and rosin. When rosin is present, it is desirable that the alum be added before the retention agent. In this way, when rosin is used, a rosin-sized filled paper sheet may be obtained. Alternatively, the paper sheet may be surfacesized after it has been formed by the application of aqueous dispersions or emulsions of waxes, higher aliphatic ketene dimers, or the like.

In the examples which are illustrative of the invention, the parts and percentages given are by weight unless otherwise noted. In Examples 1 to 8, approximately 0.10% pulp suspensions were filtered to form the sheet and basis weights were in the range of 40 to 50 lbs. The percent of retention in these examples was determined from the turbidity of the filtrates. In Example 9, 0.027% pulp suspensions were filtered to form the sheet and basis weights were in the range of 36 to 42 lbs. The percent of retention in this example was determined from the ash content of the final sheet.

Example 1 To an aqueous suspension containing 1.0% of unbleached kraft fiber and 20% of clay (on the weight of fiber), there was added 0.11% (on fiber) of the hydroacetate salt of a homopolymer of fl-(N,N-dimethylamino)ethyl methacrylate having a viscosity average molecular weight of several million as indicated by determination of its reduced viscosity 1% in water) of 234 deciliters per gram. The suspension was diluted with water to 0.09% pulp and had a pH of 6.4. On deposition of the pulp, about of the clay was retained in the sheet. The use of 3.9% alum (on fiber) gave a pH of 4.95 and served to retain only about 68% of the clay.

Example 2 Substitution of 0.11% (on fiber) of the ethylene oxide. quaternary of the homopolymer of Example 1 gave a pH of 6.7 and retention of about 90% to. 95% of the clay.

Example 3 To separate portions of an aqueous suspension containing about %-of bleached sulfite fiber and 5% (on fiber) of rutile titanium dioxide, there were added 0.3% (on fiber) of each of the polymers of Examples 1 and 2. The suspensions were diluted with water to 0.09% pulp and the pHs were 5.8 and 5.9 respectively. Substantially 90% retention was obtained in both cases,

' whereas the substitution of alum (even at 1.1% on fiber and a pH of 5.35) provided less than 10% retention; the substitution (at 0.03% and at 0.06%) of polyacrylamide having a molecular weight of several million gave pHs of 5.8 and provided less than 10% retention; and the use of 0.03% (on fiber) of a condensate of urea, formaldehyde, and triethylenetetramine gave a pH of 5.75 and provided only about 40% retention.

Example 4 (a) To an aqueous suspension containing 1.2% of bleached sulfite fiber, 8.3% (on fiber) of rutile titanium dioxide, 1.7% of rosin size and 2.8% (on fiber) of alum there was added 0.023% (on fiber) of the quaternary polymer of Example 2. The suspension was diluted to 0.11% and adjusted to a pH of 4.4 with H SO sheeting, about 80% retention of titanium dioxide is obtained.

(b) 80% retention was obtained when the retention agent was replaced by the same amount of the polymer of Example 1.

(c) 54% retention was obtained when there was substituted a polymer like that of Example 1 but of lower molecular weight, yet greater than 100,000 as indicated by a reduced viscosity (1% in Water) of 26.5 deciliters per gram.

(d) About 65% retention was obtained when there 'was substituted 0.023% (on fiber) of the hydroacetate of a copolymer of 30 weight percent of ethyl acrylate with 70 weight percent of fi-(N,N-dimethylamino)ethyl methacrylate having a reduced viscosity (1% in water) of 147 deciliters per gram.

Example 5 To an aqueous suspension containing 1.2% of bleached sulfite fiber and 8.3% (on fiber) of rutile titanium dioxide at a pH of 9, there was added 0.7% (on fiber) of the quaternary compound of Example 2. On dilution to 0.11% pulp, the pH was 9.05. On sheeting, about 90% to 95% retention was obtained.

When no retention agent was added, the pH of the 0.11% suspension was 9.11 and less than 40% retention was obtained.

Example 6 (a) To an aqueous suspension containing 1.0% of bleached sulfite fiber and 20% (on fiber) of calcium carbonate (dispersed with 0.15% on the weight of calcium carbonate of the sodium salt of a copolymer of maleic anhydride and diisobutylene), at a pH of about 9, there was added 0.028% (on fiber) of the polymer of Example 4(a) having a molecular weight above 100,000. The suspension was diluted to 0.09% pulp and had a. pH of 8.65. On sheeting, about 70% retention of the calcium carbonate was obtained.

(b) When 0.028% of the quaternary polymer of Example 2 was substituted, the pH was 8.98 and about 90% retention was obtained. 4

(c) With no added retention agent, the pH of the 0.09% suspension was 9.07 and about 10% retention was obtained.

" Example 7 To an aqueous suspension containing 1.00% of bleached sulfite pulp and 40% (on fiber) of calcium carbonate (dispersed with 0.15% on the weight of calcium carbonate of the sodium salt of a copolymer of maleic anhydridev and diisobutylene), at a pH of about 9, there was added 0.056% (on fiber) of the quaternary polymer of Example 2. On dilution to 0.09% pulp, the pH was On sheeting, about retention was efifected.

Without a retention agent, the pH of the 0.09% suspension was 8.98 and about 10% retention was obtained.

Example 8 Bleached sulfite was beaten to 420 cc. Canadian freeness and treated with 10% titanium dioxide and 2% rosin. Three percent of alum was added at the disintegrator. At this point, a portion designated pulp A was sheeted. The remainder was divided into two aliquot portions. In one designated pulp B, 0.10% (on fiber) of the polymer of Example 1 was mixed in, and in the other designated pulp C 0.10% of the polymer of Example 2 was mixed in. These pulps were sheeted. The results were as follows:

Pulp: Percent retention A 20 By the use of the retention agents of the present invention, filled papers may be deposited through a wide pH range with excellent retention of the filler, and it is possible to produce more highly filled papers with greatly reduced losses of filler or pigment in the white-water. As pointed out before, the versatility of the retention agents in respect to the pH conditions of deposition adapts the filled papers obtained by the present invention to be surface-sized by a wide variety of materials, including waxes and higher aliphatic ketene dimers.

It is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

We claim:

1. A process for making filled papers andthe like which comprises depositing on a foraminous forming surface an aqueous suspension of cellulose fibers and a water-insoluble inorganic filler, said suspension having a pH between about 3 and 12 and containing 0.01 to 0.5 by weight of the fibers and containing dissolved therein about 0.01 to 1% by weight, based on the weight of fiber, of a water-soluble homopolymer of B- (N,N-dimethylamino)ethy1 methacrylate quaternized by ethylene oxide, said homopolymer having a molecular weight of several million.

2. A process for making filled papers and the like which comprises depositing on a foraminous forming surface an aqueous suspension of cellulose fibers and a waterinsoluble inorganic filler, said suspension having a pH on the alkaline side and containing 0.01 to 0.5% by weight of the fibers and containing dissolved therein about 0.01 to 1% by weight, based on the weight of fiber, of

a water-soluble homopolymer of B-( N,N-.dimethyl amino)ethyl methacrylate quaternized by ethylene oxide, said homopolymer having :a molecular weight of several million. p l

3. A process as defined'in claim 2 in which the pH is from 8.65 to 10. 4. A process for making filled papers and the like whichcomprisesdepositing on a foraminous forming surface an aqueous suspension of cellulose fibers and'a water-insoluble inorganic filler, said suspension having a pH between about 3 and 12 and containing 0.01 to 0.5% by weight of the fibers and containing dissolved therein about 0.01 to 1% by weight, based on the weight of fiber, of a water-soluble polymer of polymerizable mono- 8 ethylenically unsaturated molecules comprising at least 10 mole percent of fi-(N,N-dimethylamino)ethyl methacrylate quaternized by ethylene oxide, said polymer having a molecular weight of several million.

"Refereuces Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR MAKING FILLED PAPERS AND THE LIKE WHICH COMPRISES DEPOSITING ON A FORAMINOUS FORMING SURFACE AN AQUEOUS SUSPENSION OF CELLULOSE FIBERS AND A WATER-INSOLUBLE INORGANIC FILLER, SAID SUSPENSION HAVING A PH BETWEEN ABOUT 3 AND 12 AND CONTAINING 0.01 TO 0.5% BY WEIGHT OF THE FIBERS AND CONTAINING DISSOLVED THEREIN ABOUT 0.01 TO 1% BY WEIGHT, BASED ON THE WEIGHT OF FIBER, OF A WATER-SOLUBLE HOMOPOLYMER OF 8(N,N-DIMETHYLAMINO)ETHYL METHACRYLATE QUATERNIZED BY ETHYLENE OXIDE, SAID HOMOPOLYMER HAVING A MOLECULAR WEIGHT OF SEVERAL MILLION. 